Fire Nation Palace

This land enters tapped unless you control a basic land.
{T}: Add {R}.
{1}{R}, {T}: Target creature you control gains firebending 4 until end of turn. (Whenever it attacks, add {R}{R}{R}{R}. This mana lasts until end of combat.)

The Last Agni Kai

Target creature you control fights target creature an opponent controls. If the creature the opponent controls is dealt excess damage this way, add that much {R}.
Until end of turn, you don't lose unspent red mana as steps and phases end.

Persist

Return target nonlegendary creature card from your graveyard to the battlefield with a -1/-1 counter on it.

Aang's Journey

Kicker {2} (You may pay an additional {2} as you cast this spell.)
Search your library for a basic land card. If this spell was kicked, instead search your library for a basic land card and a Shrine card. Reveal those cards, put them into your hand, then shuffle.
You gain 2 life.

Zhao, the Moon Slayer

Menace
Nonbasic lands enter tapped.
{7}: Put a conqueror counter on Zhao.
As long as Zhao has a conqueror counter on him, nonbasic lands are Mountains. (They lose all other land types and abilities and have "{T}: Add {R}.")

Octopus Form

Target creature you control gets +1/+1 and gains hexproof until end of turn. Untap it. (It can't be the target of spells or abilities your opponents control.)

Thousand-Year Storm

Whenever you cast an instant or sorcery spell, copy it for each other instant and sorcery spell you've cast before it this turn. You may choose new targets for the copies.

Riveteers Overlook

When this land enters, sacrifice it. When you do, search your library for a basic Swamp, Mountain, or Forest card, put it onto the battlefield tapped, then shuffle and you gain 1 life.

Firebending Lesson

Kicker {4} (You may pay an additional {4} as you cast this spell.)
Firebending Lesson deals 2 damage to target creature. If this spell was kicked, it deals 5 damage to that creature instead.

Crashing Wave

As an additional cost to cast this spell, waterbend {X}. (While paying a waterbend cost, you can tap your artifacts and creatures to help. Each one pays for {1}.)
Tap up to X target creatures, then distribute three stun counters among any number of tapped creatures your opponents control. (If a permanent with a stun counter would become untapped, remove one from it instead.)

Deflecting Swat

If you control a commander, you may cast this spell without paying its mana cost.
You may choose new targets for target spell or ability.

Opal Palace

{T}: Add {C}.
{1}, {T}: Add one mana of any color in your commander's color identity. If you spend this mana to cast your commander, it enters with a number of additional +1/+1 counters on it equal to the number of times it's been cast from the command zone this game.

Ozai, the Phoenix King

Trample, firebending 4, haste
If you would lose unspent mana, that mana becomes red instead.
Ozai has flying and indestructible as long as you have six or more unspent mana.

Sokka, Bold Boomeranger

When Sokka enters, discard up to two cards, then draw that many cards.
Whenever you cast an artifact or Lesson spell, put a +1/+1 counter on Sokka.

Azula, On the Hunt

Firebending 2 (Whenever this creature attacks, add {R}{R}. This mana lasts until end of combat.)
Whenever Azula attacks, you lose 1 life and create a Clue token. (It's an artifact with "{2}, Sacrifice this token: Draw a card.")

Bender's Waterskin

Untap this artifact during each other player's untap step.
{T}: Add one mana of any color.

Boomerang Basics

Return target nonland permanent to its owner's hand. If you controlled that permanent, draw a card.

Consider

Surveil 1. (Look at the top card of your library. You may put it into your graveyard.)
Draw a card.

Terramorphic Expanse

{T}, Sacrifice this land: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Blasphemous Act

This spell costs {1} less to cast for each creature on the battlefield.
Blasphemous Act deals 13 damage to each creature.

Cunning Maneuver

Target creature gets +3/+1 until end of turn.
Create a Clue token. (It's an artifact with "{2}, Sacrifice this token: Draw a card.")

Path of Ancestry

This land enters tapped.
{T}: Add one mana of any color in your commander's color identity. When that mana is spent to cast a creature spell that shares a creature type with your commander, scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Swat Away

This spell costs {2} less to cast if a creature is attacking you.
The owner of target spell or creature puts it on their choice of the top or bottom of their library.

Hama, the Bloodbender

When Hama enters, target opponent mills three cards. Exile up to one noncreature, nonland card from that player's graveyard. For as long as you control Hama, you may cast the exiled card during your turn by waterbending {X} rather than paying its mana cost, where X is its mana value. (While paying a waterbend cost, you can tap your artifacts and creatures to help. Each one pays for {1}.)

Lightning Strike

Lightning Strike deals 3 damage to any target.

Fire Lord Ozai

Whenever Fire Lord Ozai attacks, you may sacrifice another creature. If you do, add an amount of {R} equal to the sacrificed creature's power. Until end of combat, you don't lose this mana as steps end.
{6}: Exile the top card of each opponent's library. Until end of turn, you may play one of those cards without paying its mana cost.

Everlasting Torment

Players can't gain life.
Damage can't be prevented.
All damage is dealt as though its source had wither. (A source with wither deals damage to creatures in the form of -1/-1 counters.)

Price of Freedom

Destroy target artifact or land an opponent controls. Its controller may search their library for a basic land card, put it onto the battlefield tapped, then shuffle.
Draw a card.

North Pole Patrol

{T}: Untap another target permanent you control.
Waterbend {3}, {T}: Tap target creature an opponent controls. (While paying a waterbend cost, you can tap your artifacts and creatures to help. Each one pays for {1}.)

Realm of Koh

This land enters tapped unless you control a basic land.
{T}: Add {B}.
{3}{B}, {T}: Create a 1/1 colorless Spirit creature token with "This token can't block or be blocked by non-Spirit creatures."

Sol Ring

Ty Lee, Artful Acrobat

Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
Whenever Ty Lee attacks, you may pay {1}. When you do, target creature can't block this turn.

Ty Lee, Chi Blocker

Flash
Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
When Ty Lee enters, tap up to one target creature. It doesn't untap during its controller's untap step for as long as you control Ty Lee.

Island

Infernal Grasp

Destroy target creature. You lose 2 life.

Fists of Flame

Draw a card. Until end of turn, target creature gains trample and gets +1/+0 for each card you've drawn this turn. (A creature with trample can deal excess combat damage to the player or planeswalker it's attacking.)

Collective Inferno

Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.)
As this enchantment enters, choose a creature type.
Double all damage that sources you control of the chosen type would deal.

Agna Qel'a

This land enters tapped unless you control a basic land.
{T}: Add {U}.
{2}{U}, {T}: Draw a card, then discard a card.

Diresight

Surveil 2, then draw two cards. You lose 2 life. (To surveil 2, look at the top two cards of your library, then put any number of them into your graveyard and the rest on top of your library in any order.)

Watery Grasp

Enchant creature
Enchanted creature doesn't untap during its controller's untap step.
Waterbend {5}: Enchanted creature's owner shuffles it into their library. (While paying a waterbend cost, you can tap your artifacts and creatures to help. Each one pays for {1}.)

Negate

Iroh's Demonstration

Choose one —
• Iroh's Demonstration deals 1 damage to each creature your opponents control.
• Iroh's Demonstration deals 4 damage to target creature.

Fire Lord Azula

Firebending 2 (Whenever this creature attacks, add {R}{R}. This mana lasts until end of combat.)
Whenever you cast a spell while Fire Lord Azula is attacking, copy that spell. You may choose new targets for the copy. (A copy of a permanent spell becomes a token.)

Command Tower

{T}: Add one mana of any color in your commander's color identity.

Accumulate Wisdom

Look at the top three cards of your library. Put one of those cards into your hand and the rest on the bottom of your library in any order. Put each of those cards into your hand instead if there are three or more Lesson cards in your graveyard.

Azula, Cunning Usurper

Firebending 2 (Whenever this creature attacks, add {R}{R}. This mana lasts until end of combat.)
When Azula enters, target opponent exiles a nontoken creature they control, then they exile a nonland card from their graveyard.
During your turn, you may cast cards exiled with Azula and you may cast them as though they had flash. Mana of any type can be spent to cast those spells.

Mai, Scornful Striker

First strike
Whenever a player casts a noncreature spell, they lose 2 life.

Sword of Vengeance

Equipped creature gets +2/+0 and has first strike, vigilance, trample, and haste.
Equip {3}

Mountain

Raven Eagle

Flying
Whenever this creature enters or attacks, exile up to one target card from a graveyard. If a creature card is exiled this way, create a Clue token. (It's an artifact with "{2}, Sacrifice this token: Draw a card.")
Whenever you draw your second card each turn, each opponent loses 1 life and you gain 1 life.

Chain Reaction

Chain Reaction deals X damage to each creature, where X is the number of creatures on the battlefield.

Swiftfoot Boots

Equipped creature has hexproof and haste. (It can't be the target of spells or abilities your opponents control. It can attack and {T} no matter when it came under your control.)
Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)

Sozin's Comet

Each creature you control gains firebending 5 until end of turn. (Whenever it attacks, add {R}{R}{R}{R}{R}. This mana lasts until end of combat.)
Foretell {2}{R} (During your turn, you may pay {2} and exile this card from your hand face down. Cast it on a later turn for its foretell cost.)

Lo and Li, Twin Tutors

When Lo and Li enter, search your library for a Lesson or Noble card, reveal it, put it into your hand, then shuffle.
Noble creatures you control and Lesson spells you control have lifelink.

Ozai's Cruelty

Ozai's Cruelty deals 2 damage to target player. That player discards two cards.

It'll Quench Ya!

Counter target spell unless its controller pays {2}.

Frantic Search

Draw two cards, then discard two cards. Untap up to three lands.

Ashling, Rimebound

Whenever this creature transforms into Ashling, Rimebound and at the beginning of your first main phase, add two mana of any one color. Spend this mana only to cast spells with mana value 4 or greater.
At the beginning of your first main phase, you may pay {R}. If you do, transform Ashling.

Ashling, Rekindled

Whenever this creature enters or transforms into Ashling, Rekindled, you may discard a card. If you do, draw a card.
At the beginning of your first main phase, you may pay {U}. If you do, transform Ashling.

Ashling, Rekindled // Ashling, Rimebound

Ifnir Deadlands

{T}: Add {C}.
{T}, Pay 1 life: Add {B}.
{2}{B}{B}, {T}, Sacrifice a Desert: Put two -1/-1 counters on target creature an opponent controls. Activate only as a sorcery.

Arcane Signet

Thriving Isle

This land enters tapped. As it enters, choose a color other than blue.
{T}: Add {U} or one mana of the chosen color.

Thriving Bluff

This land enters tapped. As it enters, choose a color other than red.
{T}: Add {R} or one mana of the chosen color.

Solstice Revelations

Exile cards from the top of your library until you exile a nonland card. You may cast that card without paying its mana cost if the spell's mana value is less than the number of Mountains you control. If you don't cast that card this way, put it into your hand.
Flashback {6}{R} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Evolving Wilds

Chimil, the Inner Sun

Spells you control can't be countered.
At the beginning of your end step, discover 5. (Exile cards from the top of your library until you exile a nonland card with mana value 5 or less. Cast it without paying its mana cost or put it into your hand. Put the rest on the bottom in a random order.)

Dream Harvest

Each opponent exiles cards from the top of their library until they have exiled cards with total mana value 5 or greater this way. Until end of turn, you may cast cards exiled this way without paying their mana costs.

Swamp

Thriving Moor

This land enters tapped. As it enters, choose a color other than black.
{T}: Add {B} or one mana of the chosen color.

Glen Elendra's Answer

This spell can't be countered.
Counter all spells your opponents control and all abilities your opponents control. Create a 1/1 blue and black Faerie creature token with flying for each spell and ability countered this way.